Fred W B
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| posted on 19/5/10 at 02:29 PM |
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"Plug chop" still valid?
In my 2 stroke racing days I was used to doing a "Plug chop" to check mixture:
Get a decent length of run at full throttle.
Clutch in, cut motor, stop.
Pull spark plug/s.
Check colour.
white = too lean.
light tan = perfect
grey = too rich.
black = way too rich.
I seem to recall reading that this technique is not valid with today's Unleaded petrol, as the plugs do not colour as described above? Any
experts care to comment?.
Any yes I know today we use rolling roads, laptops and sensors, but in the absence of these?
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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matt_gsxr
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| posted on 19/5/10 at 02:30 PM |
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I can tell you one thing. They still go black when its way too rich.
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tony-devon
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| posted on 19/5/10 at 02:34 PM |
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I still tune my bikes this way 
just remember that lean kills engines, rich kills plugs, I know which is the cheapest to replace
heavy is good, heavy is reliable, and if it breaks, hit them with it
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big-vee-twin
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| posted on 19/5/10 at 02:42 PM |
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Yep, still works I understand
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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ReMan
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| posted on 19/5/10 at 03:26 PM |
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Proper mechanicing
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Madinventions
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| posted on 19/5/10 at 03:29 PM |
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And they go when you're running horribly lean...!
Link to previous thread
Ed.
Mojo build diary: http://www.madinventions.co.uk
Solo music project: Syrrenfor http://www.reverbnation.com/syrrenfor
View my band website:
http://www.shadowlight.org.uk
http://www.eastangliankitcars.co.uk/
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BenB
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| posted on 19/5/10 at 03:39 PM |
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The Haynes manual for the ST1100 still talk about the chop being used to tune....
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atspeed racing
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| posted on 19/5/10 at 04:21 PM |
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A plug cut would tell you the average fueling, and could be a help.
If you looked at a plotted dyno sheet, if the mixture is a little on the lean or rich side at a certian RPM, you would see a slight fall in the BHP
and torque. You would never see this on a plug cut and would never know.
We have seen 5 BHP on a 100BHP car at lower RPM, we corrected this and the car sounded no different than it did before.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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RichardK
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| posted on 19/5/10 at 06:00 PM |
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Yep that how I take a look at the mixture on my lads bikes, still works for me.
Cheers
Rich
Gallery updated 11/01/2011
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norfolkluego
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| posted on 19/5/10 at 06:00 PM |
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quote:
Originally posted by matt_gsxr
I can tell you one thing. They still go black when its way too rich.
I can confirm that and that they go a nice tan biscuity colour when OK, worryingly my car gives me two plugs of each colour at the moment, should
balance out shouldn't it
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Fred W B
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| posted on 19/5/10 at 06:48 PM |
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Thanks for the speedy responses guys.
Trick with the two strokes always was to get as close to lean as you dare, as the engine made best power then.
There was a fashion in the kart racing at a stage to run the top end mixture so lean it would just about sieze at the end of the longest straight,
this was prevented by momenterialy choking the air intake with your hand (to pull in extra fuel) just before the critical point each lap.
Cheers
Fred W B
[Edited on 19/5/10 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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dhutch
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| posted on 19/5/10 at 07:59 PM |
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quote:
Originally posted by matt_gsxr
I can tell you one thing. They still go black when its way too rich.
Its not untrue!
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austin man
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| posted on 19/5/10 at 09:01 PM |
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this has been the method that I have set my twin 40's on a 1.8 zetec along with balancing the carbs and I have done 7000 trouble free miles. My
old many swore by this method, he was a mechanic for 50 years
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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